Jeremy D Isaacs
St Georges University of London, UK
Dr Jeremy Isaacs is a consultant neurologist at St George’s Hospital and Kingston Hospital and Honorary Senior Lecturer at St George’s University of London. He studied medicine at Cambridge and UCL. His PhD was on the immunology of Creutzfeldt-Jakob disease (CJD). His current research interests are in functional cognitive disorders, delirium and clinical trials in Alzheimer’s disease and vascular dementia. Dr Isaacs was a member of the NICE 2018 dementia clinical guideline committee. He is deputy clinical director of the NHS England (London) Dementia Clinical Network where he leads the London memory network, memory service audit and pathway streamlining programme.
Functional cognitive disorder (FCD) describes cognitive dysfunction in the absence of an organic cause. It is increasingly prevalent in memory clinics yet its key neuropsychological features have not been well studied. We hypothesised that cognitive profiles in fibromyalgia (FM), chronic fatigue syndrome (CFS) and functional neurological disorders (FNDs) would provide a template for characterising FCD.
We conducted a systematic review of studies with cognition-related outcomes in FM, CFS and FND. We selected 52 studies on FM, 95 on CFS and 39 on FND. We found high rates of subjective cognitive symptoms, including forgetfulness, distractibility and word-finding difficulties, but inconsistent objective neuropsychological deficits. Objective deficits were reported, including poor selective and divided attention, slow information processing and vulnerability to distraction. In some studies, cognitive performance was inversely correlated with pain, exertion and fatigue. Performance validity testing demonstrated poor effort in only a minority of subjects. Patients with CFS reported a heightened perception of effort in during testing.
The available data suggest that the cognitive profiles of FM, CFS and non-cognitive FND are similar to the proposed features of FCD, suggesting common mechanistic underpinnings. Similar findings have been reported in patients with mild traumatic brain injury and whiplash. We hypothesise that pain, fatigue and excessive interoceptive monitoring produce a decrease in externally directed attention. This increases susceptibility to distraction and slows information processing, interfering with cognitive function, in particular multitasking. Routine cognitive processes are experienced as unduly effortful. This may reflect a switch from an automatic to a less efficient controlled or explicit cognitive mode, a mechanism that has also been proposed for impaired motor control in FND. These experiences might then be overinterpreted due to memory perfectionism and heightened self-monitoring of cognitive performance.
We are currently testing several hypotheses generated by this review in a cohort of patients with FCD.